erts: don't loop indefinitely on --enable-pgo
erts: don't loop indefinitely on --enable-pgo

In https://bugs.gentoo.org/686786 gcc-9.1.0 exposed
a bug in erts/configure: if compiler does not support
PGO flags the configure process calls 'yes = yes'
(indefinite loop) instead of 'test yes = yes'.

The change does not fix gcc-9.1.0 PGO detection but
fixes ./configure termination.

Reported-by: Dennis Schridde
Bug: https://bugs.gentoo.org/686786
Signed-off-by: Sergei Trofimovich <110fdadc76b6bce16977f568bdb4723eaed6fb3f@gentoo.org>

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